In conventional telephone networks (known colloquially as “POTS”—plain old telephone system) the end-to-end connection between a telephone exchange and customer premises is made by a branched network of wires along which an electric current can be transmitted, the current being modulated to provide analogue voice signals, and also digital pulses as used for dialing numbers, activating bells or other alerts (“ringing current”) and, more recently, for data transmission such as facsimile transmissions or computer connections to the “Internet”. The existence of an end-to-end electrical connection in conventional systems allows simple customer equipment (specifically telephone handsets) to be powered at low voltage from a power supply at the exchange. This was a particular advantage in the early development of telecommunications networks, when mains power supplies were less widespread than they have since become. It remains a useful feature that the telephone equipment is powered independently of the mains power supply to the customer premises, as in the event of failure of that supply, a user can still use the telephone to report the fact to the power supply company. Indeed, the user instructions for cordless telephones (which require a mains supply for the base station) strongly advise users to also maintain a fixed (wired-in) telephone on the premises for use in such eventualities.
The presence of an end-to-end wired network has also allowed intermediate elements (herein referred to as “nodes”) in the branched network to use electrical power delivered over the wires from elsewhere in the network. Many of these points are either in public locations (the familiar roadside “cabinets”, and the “distribution points” which are typically positioned at the top of wooden poles from where the “final drop” wire is connected to the customer premises). These nodes are unattended and often either in remote locations, where it may be difficult to arrange a mains power supply, or in public locations where the presence of a mains power supply could constitute a hazard to some members of the public, and a temptation to others. Hitherto, such nodes have had relatively modest power requirements, and provision of a low-voltage power supply from the exchange has been sufficient to avoid the need for a mains power supply to be provided to these nodes.
For the avoidance of doubt, the term “node” refers to elements within the network, as distinct from the “network termination point” (also known as the “network interface device” NID) located on a customer's premises which provides the interface between the network operator's equipment and that of the customer.
Modern developments in telephony have made this simple pattern less practical in recent times. In particular, the use of electromagnetic media (e.g. microwave or, more commonly, optical fibre) is already well-established in the trunk network (between exchanges) and is now becoming established in the local distribution network. Such arrangements are sometimes known as “fiber to the curb”, only the “final drop” from distribution point to customer' premises remaining as conventional copper wire. The use of such connections allows much greater capacity. It is also cheaper, as copper is relatively more expensive compared with optical fibre (or indeed microwaves). However, electrical power cannot be provided to the network nodes over such media.
WO09138711A (see FIG. 1) describes an electrically powered node (3) of a telecommunications system which has a battery power backup (37) associated with its power control unit (33). Under normal conditions it is maintained fully charged by means of trickle currents from the mains power feeds (14) connected to each of a number of customer equipments (4), by way of the “final drop” (10) to the distribution point. These trickle currents are controlled by the respective power control units (33, 43), to prevent overcharging. Using an electrical copper connection (19) provided in parallel with the fibre connection (9), a battery backup (27) can also be maintained in nodes (2) further towards the exchange. These feeds are made reversible, so that if a power outage removes the power supply (14) from the customer premises (4), a “lifeline” plain telephone service between the exchange (1) and the telephone handset (5) is maintained over the connections (9, 10, 13), using the local battery backup (27, 37) in the remote nodes (2, 3). By limiting the service to simple telephony, the battery power (27, 37, 47) can be sufficient to maintain the service for a reasonable duration. The power management systems (23, 33, 43) can be used to transfer charge from one battery (27, 37) to another over the network according to the usage, or remaining life, of each battery (27, 37, 47).
U.S. Pat. No. 6,665,404 describes an apparatus for remote line powering in a telecommunication network, the apparatus including a plurality of line pair terminations terminating a corresponding plurality of line pairs that are suitable for use in the telecommunication network, the line pairs being operative to convey electric power supplied by a corresponding plurality of power sources, and an electric power aggregator operative to aggregate the electric power supplied via the plurality of line pairs to provide electric power suitable for powering an appliance, and to control that the electric power supplied via each line pair of the plurality of line pairs does not exceed a pre-defined threshold.
The apparatus additionally includes an alarm and logic unit operative to generate an alarm indicating a low voltage output level. The alarm and logic unit may further be operative to generate an indication indicating that electric power is not received over at least one line pair.
U.S. Pat. No. 7,359,647B describes a technique for transmitting and receiving power over optical fiber—in particular, a power over fiber system in which an optical network transmits electrical power via an optical signal and also transmits data within the optical network. The optical signals include a high frequency data portion that comprises the data to be transmitted, and either a constant or low frequency power signal portion. The optical signal is received and converted into an electrical signal by a photodetector/photodiode that is electrically filtered to separate the data signal from the power signal. The data signal is then processed using known techniques. The power signal can be conditioned and/or regulated, if necessary, and provided either directly to a terminal piece of equipment to provide all the required power thereto, or may be combined with locally provided power to contribute at least a portion of the power required by the equipment.
To the best of the Applicant's knowledge, there is no an effective practical solution for reliable operation of an access node or any other common element not provided with a battery, in case of power outage.